The use of digital control systems for controlling vehicle systems on different types of vehicles is rapidly increasing. Such systems typically sense operating parameters and use the sensed parameters to generate control signals for the vehicle systems. However, such sensed parameters may become stale if delays occur before valid data can be generated. Further, typical sensors are unable to sense conditions ahead of the vehicle. Thus, it would be desirable to generate control signals based upon anticipated conditions ahead of the vehicle.
For example, speed or cruise control systems are used to control vehicle speed in automobiles, trucks, combines, tractors and other vehicles. A typical speed control system generates a closed-loop control signal based upon a difference between a target speed set by an operator using an input device and sensed vehicle speed. The control signal is applied to a speed actuator such as a throttle valve, a governor or a continuously-variable (e.g., hydrostatic) transmission which adjusts vehicle speed to minimize the difference between the speeds.
However, the accuracy of such speed control systems can suffer since they are unable to respond to varying conditions (e.g., up-hill or down-hill slopes) along a course of travel which will affect load on the vehicle's engine until after the vehicle encounters the conditions and an error in vehicle speed has occurred. For example, vehicle speed may quickly drop as the vehicle starts to climb a steep hill before a speed control system reacts and increases torque applied to the drive train. Also, such speed control systems are unable to vary vehicle speed from a target speed under conditions where vehicle speed would be varied by a skilled driver. For example, a target speed selected for steady-state travel on flat ground may be too slow for a vehicle about to ascend a hill and too fast for a vehicle about to descend a hill. Differences between a target speed and speed which would be commanded by a skilled driver may waste time and fuel, and may cause operator discomfort. It would be desirable to have a control system for more accurately controlling vehicle speed by responding to anticipated conditions (e.g., slope) along the vehicle's course of travel.
Digital control systems can also be used to control transmissions having a variable reduction ratio between the engine speed and the speed of the driven wheels. The transmissions include automatic transmissions with gears selected in response to control signals. Gear selection typically depends upon vehicle speed and the opening of a throttle valve, and gear shift points are stored in gear shift scheduling maps accessed by control circuits which generate the control signals. Multiple shift scheduling maps may be defined for use in different conditions such as a vehicle being on up-hill, flat or down-hill slopes. The transmissions further include continuously-variable transmissions (e.g., hydrostatic transmissions) including reversible-flow, variable-displacement hydraulic fluid pumps for supplying pressurized hydraulic fluid to fixed or variable-displacement hydraulic motors. The pumps are driven by power sources such as internal combustion engines, and the rate and direction of fluid flow are controlled in a closed-loop. Thus, the hydraulic motors may be operated at varying speeds and directions.
However, such transmission control systems may not select an optimal ratio under certain conditions since they are unable to respond to varying conditions along a course of travel which will affect engine load, and the selected ratio may differ from the ratio which would be selected by a skilled driver driving a vehicle having a manual transmission. For example, the selected ratio for a vehicle traveling on a flat surface may be higher or lower than the optimal ratio if the vehicle is about to ascend or descend a hill. Differences between a selected ratio and the optimal ratio or the ratio which would be selected by a skilled driver can result in an upshift or downshift occurring too early or late, increased braking, and decreased fuel economy. Thus, it would be desirable to have a system to control a transmission by responding to anticipated conditions along the course of travel.
Digital control systems can also be used to control exchanges of energy between energy storage devices and drive trains in automobiles, trucks and other vehicles powered by fuel engines, electric motors and combinations thereof. Energy exchanges are accomplished by switches or clutches which selectively couple and uncouple energy storage devices to the drive trains. The storage devices (e.g., flywheels, batteries) are charged using external power sources (e.g., electric utility lines) before the vehicles are driven, or using excess power generated by the vehicle engine during low power demand periods, or using kinetic energy recovered during deceleration or braking (e.g., regenerative braking). Energy is released from the energy storage devices during high or peak power conditions (e.g., acceleration or up-hill travel). Using energy storage devices to selectively store and release power can be advantageous. Energy can be conserved since energy normally lost during deceleration and braking can be recovered for later use, and the engine can be run at efficient operating points for longer periods. Further, less-powerful engines can be used since a portion of peak power is supplied by the energy storage devices.
However, such energy exchange control systems are unable to optimally respond to varying conditions along a course of travel which will affect load on a drive train. For example, such control systems may fully charge and then disconnect a flywheel from the drive train during steady state travel under flat conditions such that the stored energy is available to climb the next up-hill. However, if the vehicle then starts to descend a down-hill, the excess energy being generated cannot be stored since the flywheel is already charged, and the energy is wasted. Such control systems are unable to anticipate a down-hill slope and drain energy from the flywheel before starting the descent (during which the flywheel could be re-charged using excess energy). Such control systems are further unable to anticipate the end of a trip and similarly drain the flywheel energy. The energy losses may be especially problematic in electric or hybrid vehicles where the energy available from pre-charged batteries is an important limiting design factor. Thus, it would be desirable to have a control system for an energy-exchange system which improves performance by anticipating conditions along the course of travel.
Digital control systems can also be used to control vehicle systems including clutches and differential locks. Clutches may include front-wheel or four-wheel drive clutches for selectively engaging and disengaging engines from the front or rear vehicle wheels in response to control signals. Differential locks may include intra- or inter-axle differential locks for selectively locking and unlocking wheels or axles in response to control signals. The control signals may, for example, select four-wheel drive or lock a differential as a vehicle travels up-hill or down-hill.
However, clutch or differential lock control systems may not optimally respond to varying conditions along a vehicle's course of travel which will affect engine load and traction. For example, such control systems may fail to engage a clutch or lock a differential until a vehicle has already started to climb a steep hill and the wheels have started to slip. The subsequent engagement of four wheel drive or a differential lock may be too late since the wheel slipping has already decreased ground traction. Other conditions which will affect traction include the soil's moisture content, the soil surface texture (e.g., rocky, sandy, etc.) and soil compaction. It would be desirable to have such a control system responsive to these anticipated conditions along the course of travel.
A vehicle which can be equipped with various digital control systems is an agricultural harvesting vehicle (e.g., a combine or cotton harvester). Such vehicles can be equipped with control systems for controlling vehicle or engine speed, transmission ratio, and settings for various crop processors (e.g., rotor speed, concave clearance, sieve openings, and cleaning fan speed). Other agricultural vehicles (e.g., multi-purpose tractors, sprayers, etc.) are also so equipped.
Agricultural harvesting vehicles typically include an engine which, when running efficiently (e.g., at or close to maximum horsepower), produces a finite amount of power which is applied to the propulsion system and the crop processors. To insure the crop processors receive sufficient power from the relatively fixed power budget to efficiently process crop with acceptable loss rates, it is desirable to control vehicle speed as a function of the power demand or load of the crop processors. Thus, vehicle speed is preferably reduced as a vehicle enters areas of a field with dense crop conditions (i.e., high crop yield or total crop mass flow) and increased as the vehicle enters areas with sparse conditions. Maximum efficiency is achieved by setting vehicle speed as high as possible while maintaining acceptable loss rates or threshing performance.
Other crop conditions may also affect the power demands of the crop processors. These conditions may include the crop type, the toughness of the crop, and the moisture content (i.e., biomass moisture) of the crop. Also, the vehicle's propulsion load is affected by ground conditions (e.g., soil moisture or surface texture).
The travel speed of a harvesting vehicle is often controlled by adjusting the hydraulic fluid flow rate of a continuously-variable hydrostatic transmission driven by the engine. Travel speed may be adjusted manually by the operator based upon sensed grain loss and other conditions detected by sensors (e.g., yield), and by the operator himself. However, efficiency of such control systems depends upon an operator's skill, and the need to make continual adjustments is tiresome for the operator.
Attempts have been made to automate control of the various settings of harvesting vehicles. For example, U.S. Pat. No. 4,130,980 describes a control system for automatically controlling the forward speed of a combine in response to feeder and separator loading and for reducing speed in proportion to grain losses exceeding predetermined limits. However, such control systems have been relatively inefficient because the control inputs (grain loss; crop yield; total crop mass flow; moisture content) are generated too late in the control cycle. A significant time period (e.g., 5 or 10 seconds) may be required for crop to be processed (e.g., cut, gathered, threshed, separated and cleaned) before the control inputs are sensed. During this crop passage delay, the vehicle may travel a significant distance and conditions of the crop currently being cut and processed may have changed from the conditions being sensed. For example, with a processing delay of 10 seconds and a ground speed of 3 mph, sensed crop conditions will correspond to crop that was growing 44 feet rearward of the crop being cut.
The stale sensed data adversely impacts harvesting efficiency. For example, if the sensed crop was sparse but the crop currently being cut is dense, such control systems erroneously increase vehicle speed just as more power is needed to process the crop, thereby increasing grain loss and decreasing efficiency due to overloaded crop processors. By the time the increased grain loss and increased yield signals become available to the controller, conditions may have already changed. In this situation, it would have been desirable to slow the vehicle before the dense crop was cut in order to maintain a uniform feed rate. In the opposite example, if the sensed crop was dense but the crop currently being cut is sparse, such control systems erroneously decrease vehicle speed just as crop processor load is decreasing, thereby wasting time and decreasing efficiency.
Accordingly, it would be advantageous to provide an improved control system for controlling a vehicle system. The vehicle system may include a vehicle speed actuator, transmission, energy exchanger, clutch, differential lock or crop processor. It would be desirable to provide a control system for controlling a vehicle system at least partly in response to anticipated conditions of a field, road or crop along a course of travel. Further, it would be desirable to provide a control system for controlling a vehicle system in response to an anticipated condition which will affect engine load as the vehicle moves along a course of travel. It would further be desirable to provide control of various systems in an agricultural harvesting vehicle in response to anticipated conditions of crop before such conditions have been sensed.
Anticipated conditions can correspond to positions along a course of travel at which the conditions have not been detectable in real-time by vehicle-mounted sensors as is desired for certain control purposes. Conditions forward of the current position of the vehicle have not been detectable in real-time. For example, a down-hill slope starting 100 yards forward of the current vehicle position has not been detectable. Conditions for which a significant processing time is required for sensing have also not been detectable in real-time. As explained above, for example, some crop conditions such as yield and total mass flow have not been detectable in real-time because of the processing delays required for sensing. Thus, it would be desirable to provide a control system for controlling a vehicle system which can predict an anticipated condition along a course of travel before such condition is detectable by conventional sensors.